Firstly, to understand the way in which polyoma virus causes cellular transformation. To do this we will investigate the functions and subcellular locations of the three T antigens of polyoma virus - the 90,000, 60,000 and 22,000 dalton products of the early region of polyoma virus. By the use of monospecific sera and partial purification we hope to be able to define the roles of the individual T antigens. Secondly, to investigate the mechanism by which the 60,000 dalton product of the Rous sarcoma virus sar gene (p60src) effects cellular transformation. p60src is a protein kinase with the unusual specificity of phosphorylating tyrosine. Our efforts will concentrate on identifying the intracellular targets of this protein kinase. This task will be aided by using the criterion that any substrate of p60src should contain the rare modified amino acid, phosphotyrosine.